Radio frequency identification (RFID) tags and radio frequency identification tag systems are used for identification and/or tracking of equipment or inventory such as pallets, trucks, dollies or boxes or even the whereabouts of some animals, such as livestock in certain situations. These RFID systems are radio communication systems in which communications is provided between a radio transceiver, or interrogator, and a number of small, identifying labels or tags. These tags are read while in the radiation pattern or field of the interrogator, which may be connected to a computer-based tracking system. The intent of an RFID system is to provide a reliable and secure architecture that meets a predetermined performance requirement, while minimizing the cost of the interrogator and the tags.
Conventionally, in the operation of RFID systems, the interrogator transmits to the tags using modulated radio signals, and the tags respond by transmitting modulated radio signals back to the interrogator. Specifically, the interrogator first transmits an amplitude-modulated signal to the tag. Next, the interrogator transmits a continuous-wave (CW) radio signal to the tag. The tag then modulates the CW signal using modulated back scattering (MBS) wherein the antenna is electrically switched, by the tag's modulating signal, from being an absorber of radio frequency (RF) radiation to being a reflector of RF radiation; thereby encoding the tag's information onto the CW radio signal. The interrogator demodulates the incoming modulated radio signal and decodes the tag's information message. A radio frequency identification tag system conveniently provides for reading the information from the radio frequency identification tag at a small distance using radio frequency (RF) data transmission technology. Typically, the user simply holds or places the radio frequency identification tag near a base station that transmits an excitation signal to the radio frequency identification tag powering circuitry contained on the radio frequency identification tag. The circuitry, responsive to the excitation signal, communicates the stored information from the radio frequency identification tag to the base station, which receives and decodes the information. In general, radio frequency identification tags are capable of retaining and, in operation, transmitting a substantial amount of information—sufficient information to uniquely identify individuals, packages, inventory and the like.
In one application that is relevant to the present invention, specimen containers (e.g. vials) are used conventionally in the dairy and the drug testing industries. In such industries, a unique specimen sample (e.g. milk in the dairy industry, and blood or urine in the drug testing industry) is maintained in the vial. The unique specimen must be identified and tracked. In some applications, the specimens are identified and tracked by a unique bar code. Bar codes are typically located using a hand held optical scanner. Such bar code labeling systems utilize a light beam emitted from the scanner to “read” the bar code label. These systems require a direct line of sight between the scanner and the bar-code label, thus greatly limiting their utility.
In addition, the specimen containers may be provided with access that can be gained only by producing visible evidence that the container has been opened whether by accident or on purpose (e.g. use of tape or seal). Such a container is useful in the transportation and storage of liquid specimens for example, to ensure the integrity, of the specimen. The integrity of the specimen in the vial is becoming increasingly important in the dairy industry and for drug testing. It is important to ensure the so-called “guaranteed chain of custody” of the container contents by providing a “tamper-evident” seal to the vial—to protect from being opened by unauthorized personnel who might tamper with the contents.